The present invention relates generally to imaging systems, and in particular, to volume-holographic imaging systems having the capability to return three-dimensional spatial as well as spectral information.
Volume imaging systems may be used in applications such as bio-medical investigation, industrial product inspection, military reconnaissance etc. Certain conventional imaging systems for capturing image data of, for example, a semi-translucent three dimensional sample, such as biological or chemical sample, include confocal microscopy, interferrometric profilometry, Moiré profilometry, and optical coherence tomography. The choice of imaging method depends, in part, on the required resolution, available working distance and nature of the object (e.g., reflective diffusive, semi-transparent, fluorescent etc). Such systems typically require scanning each point in an x by y scan plane for each of many scans along a z direction. Scanning along three dimensions is needed therefore, to acquire a series of planar scan images that are representative of a three dimensional sample.
Other imaging systems employ volume holograms to extract selected data from a sample. For example, U.S. Published Patent Application No. 2004/0021871 discloses a holographic imaging spectrometer that uses a volume hologram to extract a line image from a sample. As shown in FIG. 1, a volume hologram 10 having a thickness L may be recorded by interfering an object plane wave 12 with a reference plane wave 14. The volume hologram may then be used to process information from unknown complex incident waveforms. The spatial selectivity of Bragg matching in volume holograms makes it possible to selectively extract specific information from the input, and project the information onto one or more detectors. Illumination 16 is focused to form a probe point source 18 at the same wavelength as the reference and object waves 12 and 14 within a translucent three dimensional object 20 using an object lens 22. The resulting optical information may be collimated by a collimating lens 24 and directed toward the volume hologram 10 along the same direction that the object plane wave 12 approached the volume hologram 10 in recording the volume hologram. A holographic image in the form of a slit 26 that includes the optical information from the point 18 will be Bragg matched by the volume hologram and will be directed toward a collector lens 25 along the direction from which the reference plane wave approached the volume hologram during recording, but extending from the opposite side of the volume hologram as shown in FIG. 2A. The slit image 26 is created by Bragg matching, and may be projected onto a focal plane 28 of a detector. If the translucent three dimensional object 20 is moved along the y direction such that the probe point source is moved along the y axis, subsequent adjacent slices may be formed at the focal plane 28 of a detector. As shown in FIGS. 2B and 2C, a probe point source 30 may cause an image slit 32 to appear at one side of a detector surface, while a probe point source 34 and may case an image slit 34 to appear at an opposite side of a detector surface.
Scanning along the y direction, therefore, is required to form each planar scan image, and scanning along the z direction is required to develop a series of planar scan images that are representative of a three dimensional object.
There continues to be a need, therefore, for a three dimensional imaging system that does not require scanning along at least two dimensions.